This section shows frequencies allocated for radio astronomy in the European
Union. This is by international agreement. Certain scientifically important
frequency bands are kept clear of radio transmissions, allowing radio astronomers
to detect the faint signals from cosmic sources.

In practice, there is still some interference. Some of these frequency bands
are close in frequency to legal, high power transmitters. High signal
levels out of the radio astronomy bands can still desensitize radio telescope
receivers. All practical transmitters also radiate a small fraction of power
away from their allocated frequencies, called 'spurious' signals. These spurious
signals are very small, but still many times larger than the signals radio
astronomers are trying to detect. For these reasons the most sensitive radio
telescopes are as far away from civilization as possible and normally make
use of very good filters.

Radio Astronomy frequency allocations don't mean that you can ONLY use these
frequencies for radio astronomy. Any frequency for which the atmosphere is
transparent can be used. The problem is that other frequencies are assigned
to other services which might cause interference to your radio telescope.
The 88 - 108 MHz FM broadcast band is a good example of this.

Jupiter's most interesting radiation is between about 15Mhz and 30MHz. In
this range there is only one very small, officially allocated band. To study
Jupiter's radiation in this band, the radio astronomer has to contend with
transmissions from all over the world as well as computer- and television
interference. The radio astronomer is forced to work outside the allocated
frequency range and has to learn to distinguish between all kinds of noise
and that coming from Jupiter.

In most cases, interesting frequencies have been set aside for radio astronomy.
This is thanks to the hard work of radio astronomers through the years to
keep these frequencies clear of terrestrial and satellite transmissions.
In future their work will become harder as commercial demands on frequency
usage make it very difficult for regulators to justify allocating frequencies
for scientific purposes.